1. Field of the Invention
This invention relates to a new and improved process for preparing sulfonated lignins and the resulting products which are suitable for use as dispersants and additives in dyestuffs. More particularly, the invention concerns a process for preparing such sulfonated lignin dye dispersant products having improved heat stability and dispersion capabilities in disperse dyes and printing gels or pastes. The invention also concerns dye compositions containing sulfonated lignin additives.
2. The Prior Art
Dyestuff compositions generally are comprised of a dye cake, i.e., of disperse dyes or vat dyes, and a dispersant. These dyestuff compositions are widely used to color both natural and synthetic fibers. In the dyestuff composition, the dispersant serves three basic functions:
(1) It assists in reducing the dye particle to a fine size;
(2) It maintains a dispersing medium; and
(3) It is used as a diluent.
Dye dispersants are generally one of two major types, sulfonated lignins from the wood pulping industry via the sulfite or kraft processes or napthalene sulfonates from the petroleum industry.
The advantages of employing sulfonated lignins as dispersants in dyestuff compositions are based on their unique physical properties which include good capability to many dye systems, outstanding dispersant characteristics at ambient and elevated temperatures, and availability. There are, however, certain disadvantages in employing lignins, whether they are sulfite lignins or sulfonated kraft lignins, as dispersants. Negative factors in the use of such lignins as dyestuff additives relate to problems of foaming, high pH, fiber staining, poor heat stability, and high viscosity. The adverse properties are troublesome to dyers and many attempts have been made to overcome these and other disadvantages.
A number of technological developments have resulted in new methods and processes to modify sulfonated lignins to reduce the negative aspects of employing such materials as dye dispersants without simultaneously causing any major adverse effects upon those properties which render sulfonated lignins desirable as dyestuff dispersants. U.S. Pat. No. 4,001,202 to P. Dilling and G. Prazak describes a process for preparing a sulfonated lignin with improved fiber staining properties useful as a dye dispersant by reacting such lignin with an epihalohydrin. Additional patents directed to reacting or modifying lignins to make them more suitable as dye dispersants include U.S. Pat. Nos. 4,184,845 to S. Y. Lin; 4,131,564 to P. Dilling; 3,158,520 to L. A. Baisdell; 3,094,515 to K. F. Keirstead et al; 3,726,850 to Detroit; 2,680,113 to E. Adler et al; 3,769,272 to Hintz; 3,841,887 to Falkehag et al; 4,131,564 to Dilling; 4,355,996 to Dilling et al; and 4,308,203 to Lin. U.S. Pat. Nos. 2,525,433; 2,690,973; and 3,503,762 disclose the use of lignins as an additive in printing inks, pastes, and gels. The art cited is meant to show the state of the art and not intended to be all inclusive of lignin modifications.